To the Editor.—The article by Dr Ferrucci and colleagues' on catastrophic and progressive disability helps physicians to understand the disability process in older persons. However, dehydration and cognitive impairment need more emphasis.First, Ferrucci et al found that dehydration was an important diagnosis in the disability subsets. Dehydration was 1 of the 6 most frequent discharge diagnoses among both men and women who developed progressive disability, and its cumulative percentage was similar to that of pneumonia and diabetes.1 In fact, approximately 1.5% of community-dwelling elderly will be hospitalized with dehydration annually.2 Drugs, diseases, and psychosocial factors that cause decreased fluid intake or increased fluid loss in older patients can predispose them to dehydration.3 Consequently, dehydration is both effect and cause with respect to disability. For instance, dehydration may contribute to disability by weakness due to electrolyte imbalance. In 1991, Medicare beneficiaries hospitalized with dehydration were identified